ticket:10017: Explain that for TimePeriod 5 hours, 37 minutes != 0 days, 5 hours, 37 minutes.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@33506 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10017: Oops forgot timeperiod.cpp

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@33507 251d0590-4201-4cf1-90de-194747b24ca1